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Geobacter: The Junk Food Connoisseurs of the Bacterial Kingdom

September 30, 2011 - 10:06am

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Colorized TEM (Transmission Electron Microscopy) micrograph of a cell of Geobacter sulfurreducens (orange) with its pili (yellow) stretching out like arms and immobilizing the uranium (black precipitate). | Image courtesy of Dena Cologgi and Gemma Reguera, Michigan State University

Bacteria may get a bad wrap, but there are certainly benefits to researching the remarkable capabilities of these often misunderstood microorganisms. A team of researchers at Michigan State University, assisted by scientists at the Energy Department's Argonne National Laboratory, has demonstrated exactly how a family of bacteria known as Geobacter use their arms to clean up nuclear waste and other toxic materials.

Geobacter are the junk food connoisseurs of the bacterial kingdom. They have a healthy appetite for all sorts of unhealthy "foods," including uranium and petroleum compounds like oil. And they also have the ability to turn a form of uranium that dissolves easily in water to a form that does not, which makes it much easier to clean up. (In the same way that it’s far easier to pluck a sugar cube out of water than dissolved sugar from a packet.)

Scientists have already been using Geobacter to pull waste out of water. The bacteria cleans up contaminated spaces through a process called bioremediation; however, scientists didn’t know how the bacteria were conducting their cleanups, at least until recently. In a paper published in the Sept. 6 issue of the Proceedings of the National Academy of Sciences, the team at Michigan State University, led by Dr. Gemma Reguera, demonstrated that it is the long arms (known as pili) of Geobacter that give them their unique ability to connect to uranium particles and "pull" them out of water. These arms – which can be even longer than the bacteria themselves (imagine having an arm the length of your body… or longer!) – might be better compared to wires, since they can even conduct electricity.

What’s more remarkable – as Dr. Reguera’s team also showed – is that these electrically-conducting pili actually give Geobacter their ability to clean up uranium. They reach across space, creating an extensive network that allows the bacteria to increase their energy by connecting to multiple uranium particles. The pili also keep the particles of uranium at, well, arm’s length, which better protects the bacteria. Equipment at Argonne National Laboratory, Illinois, provided additional insights into how Geobacter works, especially through the use of the lab’s bright x-ray facility, the Advanced Photon Source.

Understanding how Geobacter’s arms work suggests new possibilities for using the bacteria to clean up larger and perhaps even more contaminated sites in the future.

This work was supported by the Office of Science and in part by the Energy Department’s Environmental Remediation Sciences Office, within the Biological and Environmental Research Program. For more information on Energy Department’s Office of Science, please go to: http://science.energy.gov/.